Effects of short-term seed treatments with multi-walled carbon nanotubes (MWCNTs) on seedling development in soil culture and of rootexposure in hydroponics were studied on soybean, considered as model plant system. At 8 days after sowing and in later stages of seedling development, stunted growth and poor fine root production were detected. More detailed investigations revealed zinc (Zn) deficiency as a major growth-limiting factor. The growth of affected plants was recovered by foliar application of ZnSO4 or by cultivation in nutrient solution supplied with soluble ZnSO4. Since Zn is an important co-factor of enzymes involved in detoxification of reactive oxygen species (ROS), such as copper-zinc superoxide dismutases, stunted plant growth in response to MWCNTs treatments may be related to oxidative damage associated with lipid peroxidation and excessive oxidative degradation of auxin as growth hormone important for lateral root formation and leaf expansion.